A porous body has been widely used for filters and the like. For example, a porous body has been used for liquid (e.g., service water or sewage) filtration devices and the like. A porous body has also been used to trap and remove fine particles contained in a dust-containing gas (e.g., exhaust gas discharged from a diesel engine).
As a method of detecting a defect in a porous body used for such purposes, a method that applies laser light to fine particles discharged from a defect in a hollow fiber membrane or a honeycomb structure, and detects the laser light scattered by the fine particles to specify the fine particle discharge position, has been proposed (see Patent Documents 1 to 3, for example).
The above-mentioned method can determine the presence or absence of a defect in a porous body and specify the position of a defect in a short period of time. Moreover, a post-treatment is easy or unnecessary. Therefore the above-mentioned method is very useful.    Patent Document 1: JP-A-6-134268    Patent Document 2: JP-A-2002-357562    Patent Document 3: JP-A-2004-286703